1. Technical Field
The present disclosure relates to electrosurgery. More particularly, the present disclosure relates to systems and methods for narrowband real impedance control for precise treatment of tissue in electrosurgery.
2. Background of Related Art
Electrosurgery involves the application of high-frequency electric current to cut or modify biological tissue during an electrosurgical procedure. Electrosurgery is performed using an electrosurgical generator, an active electrode, and a return electrode. The electrosurgical generator (also referred to as a power supply or waveform generator) generates an alternating current (AC), which is applied to a patient's tissue through the active electrode and is returned to the electrosurgical generator through the return electrode. The AC typically has a frequency above 100 kilohertz (kHz) to avoid muscle and/or nerve stimulation.
During electrosurgery, the AC generated by the electrosurgical generator is conducted through tissue disposed between the active and return electrodes. The tissue's impedance converts the electrical energy (also referred to as electrosurgical energy) associated with the AC into heat, which causes the tissue temperature to rise. The electrosurgical generator controls the heating of the tissue by controlling the electric power (i.e., electrical energy per time) provided to the tissue. Although many other variables affect the total heating of the tissue, increased current density usually leads to increased heating. The electrosurgical energy is typically used for cutting, dissecting, ablating, coagulating, and/or sealing tissue.
The two basic types of electrosurgery employed are monopolar and bipolar electrosurgery. Both of these types of electrosurgery use an active electrode and a return electrode. In bipolar electrosurgery, the surgical instrument includes an active electrode and a return electrode on the same instrument or in very close proximity to one another, usually causing current to flow through a small amount of tissue. In monopolar electrosurgery, the return electrode is located elsewhere on the patient's body and is typically not a part of the electrosurgical instrument itself. In monopolar electrosurgery, the return electrode is part of a device usually referred to as a return pad.
Some electrosurgical generators include a controller that controls the power delivered to the tissue over some period of time based upon measurements of the voltage and current near the output of the electrosurgical generator. These generators use a discrete Fourier transform (DFT) or polyphase demodulation to calculate the phase difference between measurements of the voltage and current for calculating real power and for performing calibration and compensation.
Some electrosurgical generators also calculate tissue impedance by dividing a wideband root mean square (RMS) voltage by a wideband RMS current under the assumption that the tissue is mostly resistive. Calibration and compensation techniques are employed to compensate for any gain- or phase-induced errors. However, noise in the wideband measurements of the RMS voltage and current is not attenuated. In fact, the “squaring” portion of the RMS calculations correlates the noise and adds the magnitude of the noise to the magnitudes of the RMS voltage and current. At low voltages and currents, the magnitude of the noise is even more significant with respect to the magnitudes of the RMS voltage and current, leading to inaccurate measurements of the RMS voltage and current.